Conventional electronic transmission control systems are known in which sensors detect transmission output speed, engine load, engine speed, selector lever position, and other pertinent operating conditions. A microprocessor in the electronic control unit (ECU) processes the data from these sensors in accordance with a predetermined program and calculates from them signals which are relayed to the transmission to engage a suitable gear. The selected gear is physically engaged by the energization of solenoid valves and the operation of actuators, although the driver may also position the selector lever so as to keep the transmission in low gear for special operating conditions like towing or for engine braking.
The one or more electrical circuit boards which comprise the ECU must be protected from vibration, as well as water, soil, and other contaminants which might interfere with their operation. Depending on the physical location of the ECU within the vehicle, the circuit boards must be protected to a greater or lesser extent. If, for example, the circuit boards are located in the vehicle cab or another location remote from the transmission, it may only be necessary to apply a conformal coat to protect against the effects of humidity. However, if the circuit boards are located on or near the transmission, a conformal coat is largely insufficient to protect against the more rigorous environmental conditions found there.
It has therefore been proposed to mount the circuit boards in a cover adjacent the transmission, and then apply a potting material around the circuit boards to seal the boards from the surrounding environment. This approach was employed, for instance, in early designs of Eaton Corporation's Converter Enhanced Electronically Managed Automatic Transmission (CEEMAT). A problem with potting the circuit boards directly in situ in the transmission cover is that if one of the circuit boards becomes inoperative, the entire unit, including the circuit boards and the control valving section which is frequently integral with the cover, must be replaced because it is impractical to physically gouge the board out of its potted mounting.